Functional Integration with an ``Automorphic'' Boundary Condition and Correlators of Third Components of Spins in the $XX$ Heisenberg Model
Teoretičeskaâ i matematičeskaâ fizika, Tome 136 (2003) no. 2, pp. 285-298

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For the generating function of static correlators of the third components of spins in the $XX$ Heisenberg model, we derive a new representation given by a combination of Gaussian functional integrals over anticommuting variables. A peculiarity of the resulting functional integral is that a part of the integration variables depend on the imaginary time automorphically: these variables are multiplied by a certain complex number under the shift of the imaginary time by the period. The other variables satisfy the standard boundary conditions of the fermionic/bosonic type. Functional integration results are represented as determinants of matrix operators. We finally evaluate the generating function of correlators and the partition function of the model in the zeta-function regularization. The consistency of the suggested functional definition is confirmed by calculating several correlation functions of the third components of spins at a nonzero temperature.
Keywords: functional integration, $XX$ Heisenberg model, correlators, generalized zeta function.
@article{TMF_2003_136_2_a7,
     author = {K. L. Malyshev},
     title = {Functional {Integration} with an {``Automorphic''} {Boundary} {Condition} and {Correlators} of {Third} {Components} of {Spins} in the $XX$ {Heisenberg} {Model}},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {285--298},
     publisher = {mathdoc},
     volume = {136},
     number = {2},
     year = {2003},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_2003_136_2_a7/}
}
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K. L. Malyshev. Functional Integration with an ``Automorphic'' Boundary Condition and Correlators of Third Components of Spins in the $XX$ Heisenberg Model. Teoretičeskaâ i matematičeskaâ fizika, Tome 136 (2003) no. 2, pp. 285-298. http://geodesic.mathdoc.fr/item/TMF_2003_136_2_a7/